president obama threw the switch. and mariah carey and aretha franklin performed. the president also took a moment to remender former south african president nelson mandela. saying "we are privileged to live in a world that was touched by his goodness". >> donning a new role as unicef's goodwill ambassador, world famous singer and song-writer, katy perry expressed her unconditional support for the most vulnerable children. katy's official appointment as the new unicef goodwill ambassador took place on tuesday at the organization's headquarters in new york. katy's journey with unicef began in april this year when she visited madagascar, one of the poorest countries of the world. she says the trip changed her life and inspired her songs. >> and a reminder. the little boy known as bat- kid will be back in san francisco tomorrow for a fundraiser for the 'make-a- wish' foundation. it's called "brave the bay" - and police officers and others will take part in a 5-k walk and run.also a cable car pulling contest. organizers are hoping to raise about 75-thousand dollars. 5